This invention relates to treatment of coal in open top hopper cars with asphalt emulsions and pulp mill black liquor compositions to reduce losses in transit due to the action of wind on the coal surface.
When coal is being transported in open top gondola cars in unit trains under drying weather conditions, wind action due to rapid movement of the train tends to blow dust off the surface unless some means of retarding this action is provided. Settling of coal dust near the railway tracks, particularly in populated areas, is objectionable. As much as 45% of the coal that is handled in this way may be finer than 28 mesh.
It has been proposed that the open top gondola cars be provided with covers to protect the coal against wind action. Use of fibreglass lids on cars carrying metal concentrates is known. Such lids add substantially to the tare weight of each shipment and their removal before dumping and filling of the cars requires much labour or elaborate mechanical equipment. For coal, the cost of covering is very high in relation to the value of the product shipped.
Laying of dust by treatment of coal by oils and binders is known.
U.S. Pat. No. 1,988,999 discloses a process for rendering bituminous coal permanently dustless by treatment with 2/3 to 2 gallons per ton of a composition comprising petroleum oil, water and a by-product separated from alkaline black liquor formed in the operation of sulphate or soda pulp mills. This by-product promotes wetting and penetration of the coal by the oil. The composition may be applied by sprinkling. Lignin liquors and lignosulphonic acids, which are water soluble, are specifically excluded from the operative by-products.
U.S. Pat. No. 2,431,891, which relates to a method for preparing an aqueous colloidal suspension of asphalt in water, discloses use of the suspension for spray coating of coal to render it substantially dust proof. The asphalt component is oxidized to reduce its penetration whereby discrete coal particles are coated without producing tackiness to avoid the particles undesirably sticking together.
U.S. Pat. No. 2,854,347 discloses a process for protecting fine coal in rail cars against windage losses by spraying with an aqueous emulsion of an elastomeric substance such as latex to form a thin resilient film which is intended to keep the surface intact. When the surfaces of the coal particles are dry, increasing the quantity of elastomer can be avoided by pre-wetting the surfaces with water or solutions of suitable wetting agents. Subsequent U.S. Pat. No. 3,069,293 uses an emulsion of an alkyd resin to form a protective coating on individual pieces of coal which prevents spalling. Better coatings are formed if the coal surfaces are wetted with water or with one of a variety of wetting agents such as sodium dioctylsulfosuccinate.
A method of minimizing in-transit windage losses of coal from rail cars is described by G. H. Denton et al. in Mining Congress Journal, Volume 58, September, 1972, pages 49 to 53. In this process, a latex-in-water formulation is sprayed onto the surface of coal in a car in sufficient quantity to penetrate the coal surface to a depth of 1.5 to 2.5 inches and then dry to consolidate a top layer of the coal into a flexible crust which is wind resistant. One gallon of latex concentrate in 24 gallons of water is recommended. More dilute solutions do not wet the coal satisfactorily and more concentrated solutions tend to form a strong, rubbery sheet over the surface of the coal which tends to blow off on being ruptured.